1. Field of the Invention
The present invention relates to systems and methods for controlling delivery of a pressurized flow of breathable gas to a patient and, more particularly, to an adapter or attachment for a ventilation system such as an obstructive sleep apnea (OSA) system that allows for the delivery of humidification or low pressure oxygen to the patient.
2. Description of the Related Art
As is known in the medical arts, mechanical ventilators comprise medical devices that either perform or supplement breathing for patients. The vast majority of contemporary ventilators use positive pressure to deliver gas to the patient's lungs via a patient circuit between the ventilator and the patient. The patient circuit typically consists of one or two large bore tubes (e.g., from 22 mm ID for adults to 8 mm ID for neonatal) that interface to the ventilator on one end, and a patient mask on the other end. Most often, the patient mask is not provided as part of the ventilator system, and a wide variety of patient masks can be used with any ventilator.
Current ventilators are designed to support either “vented” or “leak” circuits, or “non-vented” or “non-leak” circuits. In vented circuits, the mask or patient interface is provided with an intentional leak, usually in the form of a plurality of vent openings. Ventilators using this configuration are most typically used for less acute clinical requirements, such as the treatment of obstructive sleep apnea or respiratory insufficiency. In non-vented circuits, the patient interface is usually not provided with vent openings. Non-vented circuits can have single limb or dual limb patient circuits, and an exhalation valve. Ventilators using non-vented patient circuits are most typically used for critical care applications.
Vented patient circuits are used only to carry gas flow from the ventilator to the patient and patient mask, and require a patient mask with vent openings. When utilizing vented circuits, the patient inspires fresh gas from the patient circuit, and expires CO2-enriched gas, which is purged from the system through the vent openings in the mask. When utilizing non-vented dual limb circuits, the patient inspires fresh gas from one limb (the “inspiratory limb”) of the patient circuit and expires CO2-enriched gas from the second limb (the “expiratory limb”) of the patient circuit. Both limbs of the dual limb patient circuit are connected together in a “Y” proximal to the patient to allow a single connection to the patient mask. When utilizing non-vented single limb circuits, an expiratory valve is placed along the circuit, usually proximal to the patient. During the inhalation phase, the exhalation valve is closed to the ambient and the patient inspires fresh gas from the single limb of the patient circuit. During the exhalation phase, the patient expires CO2-enriched gas from the exhalation valve that is open to ambient.
In the patient circuits described above, the ventilator pressurizes the gas to be delivered to the patient inside the ventilator to the intended patient pressure, and then delivers that pressure to the patient through the patient circuit. Very small pressure drops develop through the patient circuit, typically around 1 cmH2O, due to gas flow though the small amount of resistance created by the tubing. Some ventilators compensate for this small pressure drop either by mathematical algorithms, or by sensing the tubing pressure more proximal to the patient.
In patients with obstructive sleep apnea (OSA), the clinical evidence for continuous positive airway pressure (CPAP) and bi-level PAP as therapy for improving the quality of life is mounting. Over the past few decades, CPAP therapy for obstructive sleep apnea has evolved into more and more sophisticated modes of therapy for various forms of sleep-disordered breathing. CPAP, as the name implies, requires the airway pressure to be constant between inspiration and expiration. In many applications, such a pressure is achieved through the use of an air compressor which is controlled in a manner as maintains the airway pressure as closely to the prescribed pressure despite the pull (inspiration) and push (exhalation) of the patient. Bi-level PAP therapy was originally conceived with the idea of varying the administered pressure between the inspiratory and expiratory cycles. In concept, such a variable pressure setting decreases the amount of pressure against which the patient exhales, thereby decreasing abdominal muscle recruitment and consequent respiratory discomfort during the expiratory cycle. Moreover, during the inspiratory cycle, the greater level of pressure assist would combat the inspiratory flow limitation suffered by the upper airway.
For patients on CPAP or bi-level therapy for OSA, there is often a need to have supplemental low pressure, low flow oxygen. A number of solutions are currently known to provide such oxygen. In one currently known, commonly used solution, the oxygen is bled directly into the mask through connection ports normally supplied in the frame of the mask itself. In another currently known, commonly used solution, the oxygen is bled using an adapter connected between the flow generator device and the usual 22 mm delivery tube.
However, these known solution present certain disadvantages which detract from their overall utility. More particularly, with regard to the former solution, the same has the disadvantage of offering poor oxygen mixing and the continuous delivery of oxygen directly into the mask even when the flow generator device is not working (e.g. stops working because of a fault or is turned off by the patient). Another disadvantage is the presence of an additional oxygen tube that connects to the mask. With regard to the latter solution, though the same has the advantage of offering a convenient location for the oxygen connection, it suffers from the disadvantage of exposing the flow generator to potentially high oxygen concentrations in the case of a high patient tidal volume that results in back flow into the device during exhalation. Normally, standard CPAP or bi-level devices are not designed to operate in an oxygen rich environment which could otherwise lead to a member of problems. The present invention addresses the deficiencies of the prior art by providing an oxygen delivery solution similar to the latter solution described above, but eliminating its aforementioned shortcomings.
For patients on CPAP or bi-level therapy for OSA, there is also often a need to have supplemental humidification provided to the patient. In normal, unassisted respiration, heat and moisture are absorbed from the exhaled air by the inner walls of the oral and nasal cavities of the patient as the air travels from the patient's lungs to the outside environment. This heat and moisture is then transferred to the inhaled air in the next breath, helping to keep the mucus membranes of the patient's lungs humidified and at the proper temperature. Mechanical ventilation bypasses this natural system, often resulting in dry air of incorrect temperature being introduced into the oral and nasal cavities, and hence the lungs of the patient. After a period of time, the respiratory tract of the ventilated patient becomes dried, often causing discomfort. Thus, one of the known disadvantages of conventional breathing circuits is that the air delivered to the patient's lungs is not at the appropriate humidity and/or temperature level.
In order to provide for proper humidity and temperature of the air in ventilator and breathing circuits, it is known to integrate a heat and moisture exchange (HME) device into the breathing circuit. Typically, HME devices are placed into the breathing circuit somewhere within the flow path of the warm, moist air which is exhaled by the patient. The exhaled air enters the HME device, where the moisture and heat are absorbed by those materials used to fabricate the same. These materials then impart the absorbed heat and moisture to the inhaled air in the next breath. The retention of warmth and high humidity helps to prevent the patient's lungs and mucus layers from drying out. Currently known HME devices generally consist of a housing that contains a layer of flexible, fibrous, gas-permeable media or material. As indicated above, this media has the capacity to retain moisture and heat from the air that is exhaled from the patient's lungs, and then transfer the captured moisture and heat to the inhaled air when the patient is inhaling with the assistance of the flow generator. The fibrous material or media in the HME device may be made of foam or paper or other suitable materials that are untreated or treated with hygroscopic material. However, in certain circumstances, the level of humidification imparted by the HME is insufficient for proper patient comfort, thus necessitating that it be supplemented with or replaced by a more robust form of humidification emanating from a humidifier integrated into the breathing circuit. The present invention also addresses the aforementioned humidification deficiencies of prior art HME devices by providing a humidification delivery solution.